At least two people have died as a powerful winter storm moves eastward across the United States, spawning tornadoes in the southern states and blanketing others with snow.
A boy and his mother were killed in Louisiana when their home was destroyed by a tornado, police say.
The massive storm also brought blizzard-like conditions to the Midwest, with roads and schools closed, and some areas with 4 feet of snow.
Some 4,500 flights have been delayed and hundreds more cancelled.
About 500,000 people in four states — Nebraska, Wyoming, South Dakota and Minnesota — are on blizzard alert, with powerful winds and heavy snow making travel difficult. Millions more across the country are subject to less severe winter weather alerts.
Severe storms are expected along the Gulf Coast, including in Louisiana, Mississippi, Alabama and parts of Florida. There are also tornado warnings in parts of Louisiana and Mississippi.
Rescuers searched for hours before finding the mother and son who died in Louisiana, police say, after a tornado destroyed the family home in a rural area near the city of Shreveport.
“We couldn’t even find the house he was describing with the address. Everything was gone,” Sheriff Steve Prator told local TV station KSLA. He added that the child’s father had reported her missing.
In the small town of Farmerville, about 100 miles (160km) away, at least 25 people were injured after a tornado hit, according to local news station KNOE.
At least a dozen tornadoes touched down in Texas, Louisiana, Oklahoma and Mississippi on Tuesday, injuring residents and destroying homes and buildings.
More were reported Wednesday as the Louisiana governor declared a state of emergency.
Most of the US is likely to feel the storm’s impact, with cold and snow forecast as it moves east over the next few days.
“It’s a pretty vigorous storm system,” Rich Otto, a meteorologist at the Weather Prediction Center told the BBC. “This is a little bigger than the normal winter storm.”
The bad weather also caused hundreds of flight disruptions at Dallas Fort Worth International Airport in Texas and Denver International Airport in Colorado over the past two days, according to FlightAware.com.
The storm also extended into Canada, bringing heavy snow and high winds to the southern prairie region, including the provinces of Saskatchewan and Manitoba.
Freezing rain and other wintry conditions are expected to hit the upper Midwest and northeastern United States Thursday, the National Weather Service said.
The storm system began hitting the United States last Friday, bringing high winds and snow to parts of California.